It is well-known that aluminosilicates, and in particular the zeolites of 4 A type corresponding to the general formula EQU Na.sub.2 O.Al.sub.2 O.sub.3.2SiO.sub.2.4.5H.sub.2 O
are generally used in detergents and cleansing agents.
These zeolites of 4 A type are interesting for application in the field of detergency in that they are capable of sequestering and fixing calcium ions from aqueous solutions; their calcium fixing power (cation exchange power) is preferably comprised within the range of from 50 to 200 mg of CaO per gram of aluminosilicate.
Due to this reason, the zeolites are valuable substitutes for sodium tripolyphosphate and are used in order to partially or completely replace the latter.
The use of zeolites of 4 A type in the preparation of detergent and cleansing agents led to the development of new technologies of preparation, which require the use of zeolites as aqueous suspension endowed with good characteristics of fluidity and storage stability, even for many days, and containing an amount of zeolite which should be as large as possible.
It is well-known that the zeolites of 4 A type are produced as a finely subdivided powder consisting of particles with an average size comprised within the range of from 0.5 to 10 micrometers.
To be used in the field of detergent and cleansing agents, zeolites of 4 A type are suspended in water and this operation is preferably directly carried out during the manufacture of the same zeolites, after their filtering and washing steps.
For the stabilization of the aqueous suspensions of zeolites--which should still be fluid also after their storage and transport, and should capable of being mixed and pumped through the normal pipes, a large number of stabilizers have been proposed in the past.
Thus, French patent N. 2,287,504 discloses suspensions of water-insoluble aluminosilicates and borosilicates, stabilized with a dispersing agent. Among such dispersing agents, organic polymeric compounds having a molecular weight higher than 1500 and containing carboxy and/or hydroxy groups, and in particular those of natural origin, such as e.g., polysaccharides, are mentioned.
French patent N. 2,512,690 discloses suspensions of zeolites of 4 A type stabilized with a non-ionic surface active agent selected from among macromolecular polymeric organic compounds containing hydroxy groups and with an alkali-metal hydroxide.
European patent application publ. N. 154,291 proposes that the stability of the aqueous suspensions containing a macromolecular polymeric organic compound comprising carboxy and/or hydroxy groups as the stabilizing agent is improved by means of the further addition of xanthan gum.
Italian patent application publ N. 20,238 A/84 proposes that the aqueous suspensions of zeolite are stabilized by means of the addition of a water-soluble resin selected from the group consisting of xanthan gum, guar gum and mixtures thereof.
The aqueous suspensions stabilized with the above cited stabilizer agents are capable of being pumped through the usual pipelines by means of the industrial pumps and are resistant to the vibrations which they are exposed to during their transport, but show the drawback that they cannot be stored without stirring for a long time period without undergoing the phenomenon of decantation. Furthermore, in the case of the aqueous suspensions stabilized by means of the above cited stabilizer agents, the settled material is hard and difficult to be removed.
In Italian patent application publ. N. 19,861 A/87, the drawbacks which affect the prior art have been overcome by using suitable stabilizing agents selected from the group consisting of special quaternary ammonium or phosponium compounds, in combination with polymers containing hydroxy groups.
Unfortunately, these products showed good suspending properties at room temperature, whereas at higher temperatures, i.e., above 50.degree. C., have displayed poorer suspending properties.
The present Applicant has found now that the aqueous suspensions of water-insoluble inorganic materials on silica basis and in finely subdivided form can be improved as regards their useful storage life, if small amounts of a partially crosslinked polymeric material are added, also at higher than room temperature values.